a) Field of the Invention
The invention is directed to a slide valve with a controllable flow section of the valve opening. The invention is especially directed to a regulating slide valve comprising a valve body having a valve opening, and a valve plate which has two side surfaces and which is displaceable along a displacement path between an initial position in which it releases the valve opening and an end position in which it completely covers the valve opening, this displacement path forming the regulating range of the valve.
b) Description of the Related Art
Slide valves in which the valve plate is located to the side of the valve opening in the opened state and is displaceable into a position in which the valve opening is covered in order to close the valve are known in various constructional forms. In slide valves which are constructed as regulating valves, the valve plate is displaceable into different intermediate positions between its starting position and its end position by means of the correspondingly constructed drive for this valve plate. Stepper motors, for example, can be used to drive the valve plate. Other known regulating slide valves serve only for regulating and they still have a certain residual conductance even when closed as far as possible. Other known regulating slide valves are completely sealable.
Usually, the valve plates of slide valves are displaceable transverse to the axis of the through-channel forming the valve opening and at least substantially in their own plane between the position in which the valve opening is released and the position in which the valve opening is covered. So-called L-movements in which a displacement is initially carried out in the plane of the valve plate and then vertical thereto after reaching its position in which the valve opening is covered, and grinding movements (with movement components diagonal to the plane of the valve plate, particularly shortly before closure of the valve), also called J-movements, are known. The displacement of the valve plate can be effected linearly or, in case of a so-called pendulum slide, the valve plate can be adjusted by a swiveling movement around an axis vertical to the valve plate.
U.S. Pat. No. 5,577,707 discloses a slide valve in which an annular seal connection piece is provided for sealing the valve plate relative to the valve body in the closed (sealed) state of the valve. The seal connection piece is mounted in the through-channel so as to be displaceable vertical to the plane of the valve plate and engages at the sealing plate in the closed and sealed state of the valve. Another slide valve of this type in which the conductance of the valve can also be regulated in addition is known from U.S. Pat. No. 5,873,562 A. This reference mentions additional references, particularly U.S. Pat. No. 3,145,969 A, which disclose seal connection pieces that can engage at the valve plate.
The minimum conductance to which the valve known from U.S. Pat. No. 5,873,562 A can be regulated is reached in the end position of the valve plate in which the valve plate completely covers the valve opening. This is the position in which the annular seal connection piece could be pressed against the valve plate (but raised from the latter) for completely sealing the valve. The remaining conductance in this position of the valve plate which completely covers the valve opening depends on the residual gap remaining between the valve plate and the valve body. The smallest gap width between the valve plate and the valve body by which this residual gap is defined is on the side of the valve plate remote of the seal connection piece, namely, between the valve plate and a surface which lies in the plane of the valve plate and which is located opposite the valve plate in an area adjoining its lateral edge. Due to manufacturing tolerances and differential pressure which can act to vanous degrees on the valve plate and can displace the latter somewhat in axial direction of the through-channel of the valve, this residual gap can not be as small as desired. When closing the valve, the valve plate should not move toward the valve body so that unwanted particles are released into the vacuum. Therefore, an appropriate quantity for the residual gap is around 1 mm, for example. The minimum conductance to which the valve can be regulated is, for example, for nitrogen) 15 l/sec.